利用测量波阻抗欧几里得距离的柔性直流输电线路后备保护方案

Backup Protection Scheme for Flexible DC Transmission Lines by Measuring Wave Impedance Euclidean Distance

行波主保护易受高阻故障的影响,电流差动保护易受分布式电容的影响,且现有主、后备保护方案之间存在较大时间空白。为解决上述问题,进一步提高保护的可靠性,提出一种基于测量波阻抗欧几里得距离的行波纵联保护新方案。通过分析柔性直流输电线路区内、外故障时,线路两侧测量波阻抗幅值及变化趋势的差异性,提出利用二进小波变换提取宽频窗测量波阻抗,并引入欧几里得距离及相似系数表达波阻抗幅值及变化趋势,最后根据欧几里得距离和相似系数区分区内、外故障。PSCAD仿真表明所提保护方案能可靠、灵敏、快速地识别区内外故障,并具有较强的耐受过渡电阻和噪声干扰的能力。

The traveling wave main protection is susceptible to the high-resistance faults,the current differential protection to the distributed capacitance,and there is a large time gap between the existing main and backup protection schemes.In order to solve the above problems and further improve the reliability of the protections,this paper proposes a new scheme of traveling wave longitudinal protection based on measuring the wave impedance Euclidean distance.By analyzing the difference between the amplitude and change trend of the measured wave impedance on both sides of the line during the internal and external faults of the flexible DC transmission lines,it is proposed to use dyadic wavelet transform to extract the wideband window to measure the wave impedance,and introduce the Euclidean distance and the similarity coefficient to express the amplitude and change trend of the wave impedance.Finally,the internal and external faults are distinguished according to the Euclidean distance and the similarity coefficient.The PSCAD simulation verifies that the protection principle can identify the internal and external faults reliably,sensitively and quickly,and it has a strong ability to withstand the transition resistance and noise interference.